It's no coincidence that McDonald's, Carl's Jr., and Wendy's have each rolled out a new fish option on their menus around the time of Lent. In time for St. Patrick's Day, participating Micky D locations also offer the Shamrock Shake, a limited-time mint milkshake. Fast food chains are relying more on these limited-time offers, otherwise known as LTO's, around certain holidays as part of a grander marketing strategy, according to the Wall Street Journal.

Fast food chains have found that LTO's are more attractive to customers than deals, says WSJ. It's why there is a 25% uptick in limited-time offers across 250 chains in the United States. For some, these offers are more than just a limited-time special; they have become an annual ritual of sorts. (We feel the same about the seasonal fresh strawberry-stuffed donuts at The Donut Man in Glendora.)

The longest running LTO is the McRib sandwich, which has its share of fans and detractors. And finding a Shamrock Shake is tantamount to finding a shamrock -- enough to launch one website devoted to shake sightings around the country. In Los Angeles County, it has been seen in Burbank and La Cañada Flintridge. (Editor's note: Maybe just put some green food coloring in your beer.)